Colorado’s amendment to legalize marijuana continues to lead for passage with 53% of voters saying they plan to support it to 43% who are opposed. This plays out very much as a generational issue with voters under 30 favoring it 73/25, while seniors oppose it 38/55. Every age group except seniors supports the amendment, and it has a 58/36 advantage with independents.

This is 4-point increase from PPP’s previous (September 4) poll, which showed 47% in favor and 43% opposed. This is also an increase from the October 11 Denver Post /Survey USA poll which showed 48% in favor of Amendment 64 and 43% opposed.

Amendment 64 seeks to legalize the possession, use, cultivation, and manufacture of small amounts of marijuana and goods containing marijuana. It will create the legal framework necessary to tax and regulate marijuana in a manner similar to alcohol. The Amendment states that the first $40 million in annual tax revenue will be earmarked for public school construction. More information on the Amendment, as well as the full text and ballot language, can be found on the Campaign to Regulate Marijuana Like Alcohol website.

While the numbers from the latest PPP survey may appear favorable to supporters of the Amendment, the Campaign to Regulate Marijuana Like Alcohol cautions supporters against becoming complacent. A similar measure in California, Proposition 19, led in polls until late September before the 2010 election, but was defeated 53.5% to 46.5% on election day.

Post-election analysis of Proposition 19 in California determined that the measure was probably defeated due to late-in-the-game opposition from prominent public figures in California. This is a concern for supporters of Amendment 64 in Colorado as well; Governor Hickenlooper and Denver’s Mayor Hancock, as well as several interest groups, oppose the Amendment.

On the other hand, Amendment 64 has advantages that California’s Proposition 19 did not. Many local law enforcement professionals and doctors, as well as the Colorado Democratic Party, have voiced their support for the measure.

Those in favor of Amendment 64 have a significant fundraising advantage. The Denver Post reports that over $3 million has been spent so far by groups on both sides of the issue. Groups that favor legalization are out-spending opposition groups by a 4-1 margin. However, spending by groups in favor of Proposition 19 in California was also significantly higher than spending by groups opposed, so a fundraising edge for Amendment 64 does not necessarily indicate that it will pass.

Finally, the October 25 PPP poll suggests that support for Amendment 64 is currently at its highest level yet and is trending upward. For comparison, polling for California’s Proposition 19 showed support peaking in late September 2010 and trending downward until the measure’s defeat on election day.

Colorado support for Amendment 64 compared to general support for legalizing marijuana.

According to today’s Public Policy Poll of Colorado, support for Amendment 64 has grown since the June poll. The amendment, which will be on the Colorado ballot in November, proposes to legalize and regulate growth, possession, and usage of marijuana.

Support has grown by five points to 47-38 from 46-42 in June this year. Independents now support the amendment 58-28, up thirty points from support of 49-40 in June. Democrats favor it 59-22 while Republicans support it 26-61.

15% of voters are undecided on Amendment 64, up from 12% in the June poll.

The poll also posed a more general question, asking whether marijuana should be legal or illegal. Respondents were somewhat more in favor in this situation, supporting legalization 50-42 with 8% undecided. That’s a 2-point increase from June, when respondents supported legalization 49-43.

Support for Amendment 64 and legalized marijuana by political affiliation.

The 5-point swing in favor of legalization suggests that Colorado voters are becoming more comfortable with the idea of legalizing marijuana and taxing it in a manner similar to alcohol. This could be a result of the recent pro-legalization ad campaign.

It’s also possible that a lot of this change is a result of statistical noise. The margin of error on both polls was +/-3.5%, so much of the shift could be accounted for by sampling error.

However, the 30-point shift in independent support for the amendment is suggestive. The margin of error for independents is larger than for the overall poll, due to the lower number of independents, but a shift of this magnitude likely represents increasing support in this group.

In addition, little has been heard from groups opposed to Amendment 64. The group Smart Colorado, founded by Weld County District Attorney Ken Buck, opposes the amendment but has only raised $16,000 as of the latest update.

Groups in favor of Amendment 64, including the Colorado Democratic Party and the state medical marijuana industry, have raised well over $2 million.

It is still early. The election is still three months away, and the outcome can easily change during that time. California’s latest legalization attempt, Proposition 19, was leading in polls until late September 2010. It was defeated in the 2010 midterm elections 53.5% to 46.5%.

If support for Amendment 64 continues to grow, it may become law in November. But supporters of the amendment will need to be wary of a co-ordinated opposition by special interest groups. Such opposition has defeated similar measures in Colorado and California in the past.